There are also other, derived, instance variables for each glyph which are read
when the whole glyph is read (via read_dat):

instLen

Number of bytes in the hinting instructions (Warning this variable is deprecated,
use length($g-{hints})> instead).

hints

The string containing the hinting code for the glyph

In addition there are other attribute like instance variables for simple glyphs:

For each contour there is:

endPoints

An array of endpoints for each contour in the glyph. There are
numberOfContours contours in a glyph. The number of points in a glyph is
equal to the highest endpoint of a contour.

There are also a number of arrays indexed by point number

flags

The flags associated with reading this point. The flags for a point are
recalculated for a point when it is updated. Thus the flags are not very
useful. The only important bit is bit 0 which indicates whether the point is
an on curve point, or an off curve point.

x

The absolute x co-ordinate of the point.

y

The absolute y co-ordinate of the point

For composite glyphs there are other variables

metric

This holds the component number (not its glyph number) of the component from
which the metrics for this glyph should be taken.

comps

This is an array of hashes for each component. Each hash has a number of
elements:

glyph

The glyph number of the glyph which comprises this component of the composite.

args

An array of two arguments which may be an x, y co-ordinate or two attachment
points (one on the base glyph the other on the component). See flags for details.

flag

The flag for this component

scale

A 4 number array for component scaling. This allows stretching, rotating, etc.
Note that scaling applies to placement co-ordinates (rather than attachment points)
before locating rather than after.

numPoints

This is a generated value which contains the number of components read in for this
compound glyph.

This is the number of bytes required by the glyph. It should be kept up to date
by calling the update method whenever any of the glyph content changes.

OUTLOC (P)

Location relative to the start of the glyf table. This variable is only active
whilst the output process is going on. It is used to inform the location table
where the glyphs location is, since the glyf table is output before the loca
table due to alphabetical ordering.

OUTLEN (P)

This indicates the length of the glyph data when it is output. This more
accurately reflects the internal memory form than the LEN variable which
only reflects the read file length. The OUTLEN variable is only set after
calling out or out_dat.

If you want to edit a glyph in some way, then you should read_dat the glyph, then
make your changes and then update the glyph or set the $g->{ isdirty} variable.
It is the applications duty to ensure that the following instance variables are
correct, from which update will calculate the rest, including the bounding box
information.

Reads the contents of the glyph (components and curves, etc.) from the memory
store DAT into structures within the object. Then, to indicate where the
master form of the data is, it deletes the DAT instance variable.

Generates a $self-{DAT}> from the internal structures, if the data has
been read into structures in the first place. If you are building a glyph
from scratch you will need to set the instance variable read to 2 (or
something > 1) for the update to work.

This method creates point information for a compound glyph. The information is
stored in the same place as if the glyph was not a compound, but since
numberOfContours is negative, the glyph is still marked as being a compound